One viewer recommended using hard soap on a mirror to keep it from fogging up in the bathroom. So we tested it against no treatment, and against polishing it with shaving cream, a recommendation from a viewer last year. The hard soap looked pretty good although a bit streaked. The ?no treatment? fogged up seriously. The shaving cream worked really well.
We also looked back at a previous show where we had installed a special electric pad called "See Free" on the back side of the mirror to warm up the glass and always keep it fog-free. This excellent product really works, as you can see in the clear spot indicated by the arrow. I've installed one in my own bathroom.